1. Technical Field
The present invention relates to a vehicle drive assist system in which when unmelted snow is detected on one side of a road surface, a drive assist threshold for a lane line on the other side is mitigated so that a lane departure warning or the like is not frequently activated even when a vehicle equipped the vehicle drive assist system travels nearer to the lane line on the other side.
2. Related Art
In recent years, an integrated drive assist system for actively assisting driving of a driver to improve safety of vehicles has been developed. This type of drive assist system estimates various possibilities such as a collision with a preceding vehicle, a contact with an object, and a lane departure based on a traveling environment of vehicles and a traveling state of a vehicle equipped the vehicle drive assist system ((hereinafter, may be referred to as “subject vehicle”) and outputs a warning to the driver of the subject vehicle or performs other control when it is predicted that it is not possible to maintain safety.
In general, a lane departure preventing function which is one of the functions of the drive assist system recognizes lane lines (white lines, orange lines, and the like) in front of the subject vehicle using a sensor such as a camera to estimates a traveling lane of the subject vehicle. When it is determined that the subject vehicle leaves the traveling lane of the subject vehicle, a warning is output or vehicle control is performed so as to prevent the subject vehicle from leaving the lane.
In this case, if a warning is frequently output even when the driver recognizes a lane departure direction, the driver may feel annoyed. Thus, for example, Japanese Unexamined Patent Application Publication (JP-A) No. 2011-3075 discloses a technique in which reference lines for making warning determination are set along left and right lane lines, correction amounts are set for the reference lines based on predetermined conditions, and a lane departure determination threshold is set to be offset by the correction amounts with respect to the outer and inner sides of the lane, respectively, so that the time of output a warning of lane departure matches the feeling of a driver.
When a lane line on one side of a traveling road surface is covered with snow and cannot be recognized, since the lane width decreases substantially, the driver generally decelerates the vehicle and tries to travel along the center of the road surface where no snow is left. In this case, when the drive assist system disclosed in JP-A No. 2011-3075 recognizes a lane line where no snow is left, the drive assist system sets a lane departure determination threshold based on this lane line and offsets the lane departure determination threshold by a predetermined correction amount.
However, when the lane departure determination threshold cannot be offset sufficiently with the correction amount, even when the driver already recognizes the lane departure direction, it is determined that the vehicle has left the lane, a departure warning is output or departure preventing control is performed, which makes the driver feel annoyed.